The present invention relates to an image-forming process employing photoadhesive microparticles and, more particularly, to a method wherein a layer of photoadhesive microparticles containing an image-forming agent is image-wise exposed and the microparticles are differentially transferred to an image-receiving substrate to provide an image.
Imaging methods employing microparticles are known in the art. Many of these methods rely upon xerographic methods to form the image. For example, U.S. Pat. No. 3,080,251 to Claus describes a xerographic method in which a toner comprising a color-forming composition encapsulated in a shell having triboelectric properties suitable for electrostatic deposition is image-wise electrostatically deposited on a developer sheet where the capsule is ruptured to provide an image; and U.S. Pat. No. 4,013,572 to Marsh describes a photo-fixable toner prepared from a photodegradable polymer.
U.S. Pat. No. 4,456,669 to Yubakami et al. discloses a method in which conductive particles containing a sublimable color former are electrostatically deposited on a support member according to an image signal. The color former is transferred to the paper by a heat-transfer process in which the color former is vaporized. The image is developed by reaction of the color former with a developer composition. The patent also discloses a method for forming full color images wherein the particles are coated with colored solutions to give them a color separation function. The particles are deposited on a uniformly charged photoconductive support which is exposed to light through the particle layer. Exposure selectively releases the particles from the support resulting in a particle image. This image is heated to transfer the color former and developed as discussed above.
Japanese patents 9519 and 9520 to Ricoh describe image-forming methods in which microcapsules containing a photographic color coupler are said to be photoadhesively transferred to an image-receiving sheet where the coupler is reacted with a developer to produce an image. According to the disclosure, the microcapsules are prepared by dispersing a composition containing a monomer and a color coupler in polyvinyl alcohol containing a photoinitiator. It is not clear from the disclosure that this preparation actually yields a microcapsule or how the composition exhibits photoadhesive characteristics. According to the disclosure, microcapsules in the exposed areas cure and thereby become more strongly adhered to the support upon which they are carried such that upon assembling the material with a transfer sheet and applying pressure or heat, the unexposed capsules selectively adhere to the transfer sheet.
Commonly assigned U.S. applications Ser. No. 770,538 filed Aug. 28, 1985 and Ser. No. 800,018 filed Nov. 20, 1985 also disclose image-forming methods employing microparticles. The former application discloses a process for forming images on plain paper wherein free-flowing microcapsules containing a photohardenable composition and a color precursor are deposited on a support, image-wise exposed to radiation and ruptured in contact with an image-receiving sheet to which they release the color precursor. In one embodiment, the microcapsules are designed with triboelectric properties such that they can be electrostatically maintained on the support during exposure of the microcapsules and during transfer of the color precursor.
In the latter application, a layer of microparticles formed from a photodegradable polymer containing a color precursor is image-wise exposed to actinic radiation and assembled with a developer sheet to which they release the color precursor to provide the image. This imaging system does not rely upon photoadhesion to transfer the microparticles to the image-receiving sheet.